Project Summary/Abstract: Early embryonic cells are pluripotent, possessing the transient capacity to generate all the cells of an organism. A fundamental question in developmental biology concerns identifying the epigenetic factors that underlie this temporary developmental plasticity, as well as understanding how commitment to a specific cell lineage is achieved and maintained. How embryonic pluripotency is established, and whether development coordinates the restriction of cellular plasticity with the acquisition of cell fate is poorly understood. Epigenetic phenomena refer to changes in gene expression and chromatin organization inherited through cell divisions without changing the underlying DNA sequences. Recently, studies during my postdoctoral research have uncovered an unappreciated developmental regulation of the incorporation of key molecular carriers of epigenetic information, the replication-coupled histone H3 and histone variant, H3.3, during gametogenesis that influences the epigenetic organization in the early embryo, with a lasting effect on pluripotency and lineage commitment. The goal of this Pathway to Independence Award proposal is to request support for training in order to develop expertise in, and to apply, genomic approaches while addressing the role of epigenetic regulation of plasticity during early embryonic development, as well as cell fate maintenance. K99/R00 support during this stage of my career will be transformative to my successful development as an independent researcher. The research plans and career development outlined in this proposal will take advantage of the extensive resources at Johns Hopkins University, as well as collaborate with leading experts in genomics and bioinformatics. This proposal will examine the epigenetic regulation and developmental timing of early embryonic plasticity. Specifically, during the K99 mentored phase of this award the principal investigator (PI) will combine current expertise and preliminary results generated during postdoctoral training at Johns Hopkins University, with newly developed techniques developed in the collaborator's laboratories to answer fundamental questions regarding the dynamic epigenetic mechanisms underlying embryonic plasticity and cell fate restriction. This approach promises to resolve the following specific aims 1) determine the developmental significance of H3 and H3.3 bimodal incorporation during early embryogenesis and gametogenesis, 2) characterize the genome-wide localization of H3, H3.3, and their post-translational modifications during early embryogenesis, as well as their influence on chromatin accessibility and gene expression and 3) delineate the molecular pathways that orchestrate the developmental regulation of two distinct classes of histone genes important for fertility and cell fate restriction. The completion of this training will develop my research expertise, while delineating the mechanisms underlying the epigenetic regulation of embryonic plasticity, which will be applicable to the fields of reproductive biology, embryology, cellular reprogramming, and fertility.